Potential insect threats to pennycress, Thlaspi arvense (Brassicales: Brassicaceae), an emerging oilseed cover crop

Abstract Pennycress (Thlaspi arvense L.) is an annual plant in temperate regions that often grows as a weed. Pennycress is being domesticated as a new winter cover crop and oilseed crop for incorporation in the Midwest United States corn-soybean rotation, where it could offer economic and environmental benefits. While pennycress is gaining attention as a promising new crop, there remains a significant gap in understanding its interaction with insect communities and agroecosystems. This review compiles available information on insect herbivores (potential pests) and beneficial insects associated with pennycress growing in the wild (natural areas) or as a weed in agricultural areas. The limited knowledge on the response of pennycress to stressors (defoliation, stem injury and stand loss) similar to injury that could be caused by insects is also compiled here. By shedding light on the insects associated with pennycress and how pennycress might respond to injury from insect pests, this review sets the stage for further research and development of integrated pest management programs for insect pests of this new crop.


Introduction
Pennycress (Thlaspi arvense L. (Brassicales: Brassicaceae)) is native to Eurasia and is now found in Europe, Asia, North America, South America, Africa, and Australia (Best andMcIntyre 1975, Warwick et al. 2002).In the United States, pennycress was first documented in 1818 (Mitich 1996), and it has been a problematic weed for multiple crops (Warwick et al. 2002).
Pennycress is being considered as a new oil seed crop and winter cover crop (Sedbrook et al. 2014).The oil content in pennycress varies between 26% and 39% of the seed weight (Cubins et al. 2019).Pennycress meal is a beneficial source of protein as pennycress seeds have protein content ranging between 20% and 27% of the seed weight (Hojilla- Evangelista et al. 2013, Selling et al. 2013).Furthermore, pennycress is a desirable low-input winter cover crop with the potential to reduce soil erosion, take up excess nitrogen from the soil, and contribute to weed suppression (Evangelista et al. 2017, Cubins et al. 2019, Moore et al. 2020).In the Midwest United States, pennycress would likely be incorporated into the cropping systems (e.g., corn-soybean rotations) through double-or relay-cropping.For example, pennycress would be planted after the harvest of corn or possibly interseeded with the corn prior to the harvest of the corn (Cubins et al. 2019, Mohammed et al. 2020, Moore et al. 2020).The pennycress crop would overwinter, and soybean would be relay cropped into the pennycress prior to pennycress harvest or double-cropped after pennycress harvest (Johnson et al. 2017, Cubins et al. 2019, Cecchin et al. 2021).Domestication of pennycress is advancing rapidly due to the availability of a diversity of pennycress genotypes and the sequenced genome and transcriptome of this plant (Sedbrook et al. 2014, Basnet andEllison 2024).Pennycress seeds contain glucosinolates, primarily sinigrin, which provide protection against herbivores but can adversely affect some end uses for pennycress meal.Therefore, efforts are underway to lower the glucosinolate levels in pennycress seeds (Vaughn et al. 2005, Chopra et al. 2020).Domestication of crops in the past has led to increased vulnerability to insect pests (Chen and Welter 2005).The domestication of pennycress is changing its chemical defenses, which may impact its vulnerability to insect herbivores (e.g., Chen et al. 2018).The effects of pennycress domestication on insect herbivores remain unknown.
While there have been significant efforts to improve the agronomics (e.g., planting, fertilizing, and harvesting) of pennycress as a new crop (Cubins et al. 2019), there has been little focus on studying the potential insect pests that could affect this crop.Experience with related crops, such as canola and rapeseed (Brassica  Chew 1975, 1977, 1980, Lipa et al. 1977, Nakajima et Lipa et al. 1977, Smith et al. 2011 This table is updated and modified by Lipa et al. (1977).e Lipa et al. (1977) listed larva instead of nymph for the immature stage of these hemimetabolous insects.
Here, we provide a review of insects that have been reported in association with pennycress and how pennycress responds to stressors similar to the feeding injury that could be caused by some insects.This information will help to provide a foundation for the development of integrated pest management programs for this new crop.Current species names, as determined by searching the Integrated Taxonomic Information System and the National Center for Biotechnology Information (NCBI) Taxonomy Database, are listed in parentheses following the species names used in the literature.

Herbivorous Insects Associated with Pennycress
A comprehensive review of the literature found reports of herbivorous insects from 9 countries associated with pennycress (Table 1).A total of 119 species of herbivorous insects across 6 insect orders were reported in association with above-and below-ground parts of pennycress plants (Table 1).Various life stages of these species have been reported with pennycress (Table 1).For the insects that have been studied more thoroughly, a review of their interactions with pennycress is provided below.In addition to insects, twospotted spider mite (Tetranychus urticae (Koch) (Trombidiformes: Tetranychidae)), which is known as a pest of many crops, was also found on pennycress (Lipa et al. 1977).

Coleoptera
Flea beetles (Phyllotreta spp.(Coleoptera: Chrysomelidae)) are major pests of Brassicaceae crops (Warwick et al. 2002), and they have been reported feeding on leaves and flowers of pennycress in the field and in the laboratory (Lamb andPalaniswamy 1990, Soroka andGrenkow 2013).Plant death was observed in the Czech Republic for pennycress growing in the field and being attacked from emergence onward by adults of flea beetles (Štolcová 2005).Several studies have more closely examined flea beetle preferences and performance on pennycress compared to other plants.In laboratory choice tests with adults of Phyllotreta cruciferae (Goeze), feeding on B. napus, Sinapis alba L. (Brassicales: Brassicaceae), Sinapis pubescens L. (Brassicales: Brassicaceae) and Crambe glabrata DC. (Brassicales: Brassicaceae) was higher than on pennycress (Soroka and Grenkow 2013).Nonpreference resistance (i.e., antixenosis) of pennycress and S. alba has been observed for P. cruciferae (Gavloski et al. 2000).Choice tests done using leaf discs indicated that Phyllotreta armoraciae (Koch) prefers black mustard (Brassica nigra (L.) Koch (Brassicales: Brassicaceae)) and S. alba over pennycress (Nielsen et al. 1979), and that Phyllotreta nemorum (L.) and P. cruciferae prefer black mustard, radish (Raphanus sativus L. (Brassicales: Brassicaceae)), S. alba, and B. napus over pennycress (Nielsen et al. 2001).Similarly, P. cruciferae adults were found to exhibit a strong nonpreference response to pennycress compared to Brassica juncea (L.) Czernajew (Brassicales: Brassicaceae), Brassica carinata A. Braun (Brassicales: Brassicaceae), B. napus, B. rapa, and S. alba in Manitoba, Canada (Palaniswamy et al. 1997); and pennycress was only marginally acceptable to Phyllotreta striolata (F.) in Alberta, Canada (Meisner and Mitchell 1983).In no-choice conditions, survival of P. cruciferae adults on intact leaves of pennycress was as low as 9%, and adults that did survive on pennycress lost weight (Palaniswamy et al. 1997).In contrast, based on feeding experiments performed in the Czech Republic, Štolcová (2009) concluded that Phyllotreta nigripes (F.) and Phyllotreta atra (F.) do not show clear preferences among pennycress, wild mustard and B. napus.Overall, glucosinolates have been suggested as important factors for flea beetle host selection, and reducing the expression of glucosinolates in plants may change their susceptibility to being attacked by flea beetles (Soroka and Grenkow 2013).
Adults of cabbage seedpod weevil (Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae)) were found on pennycress and other Brassicaceae weeds in Alberta, Canada (Dosdall and Moisey 2004).In a mixed stand of pennycress, wild mustard (Sinapis arvensis L. (Brassicales: Brassicaceae)) and flixweed (Descurainia sophia (L.) Webb ex Prantl (Brassicales: Brassicaceae)), C. obstrictus adults were found more frequently on wild mustard, and more on buds than stems or leaves independently of plant species (Dosdall and Moisey 2004).Pennycress did not appear to support C. obstrictus larval development as none of the pennycress seed pods had larval exit holes (Dosdall and Moisey 2004).Thus, pennycress may serve as an alternative food source for C. obstrictus adults in early spring until canola crops develop inflorescences that attract adults for feeding and reproduction.
Alfalfa weevil (Hypera postica (Gyllenhal) (Coleoptera: Curculionidae)) was found to oviposit on pennycress growing as a weed in alfalfa (Medicago sativa L. (Fabales: Fabaceae)) fields in Idaho, United States (Saad and Bishop 1969).After rearing the alfalfa plants in the laboratory, eggs of H. postica were observed to hatch, but larvae did not feed on pennycress, suggesting that H. postica larvae may migrate from pennycress to alfalfa in the field (Saad and Bishop 1969).
The sap beetles (Meligethes aeneus F. (currently Brassicogethes aeneus (F.)) and M. viridescens F. (currently Brassicogethes viridescens (F.)) (Coleoptera: Nitidulidae)) are pests of Brassicaceae crops in Europe (Williams 2010), and have been reported from pennycress (Lipa et al. 1977).However, M. aeneus and M. viridescens were not found on pennycress in a field study looking at the temporal distribution and dynamics of these species across a variety of Brassicaceae crops and weeds in May-July in Estonia (Metspalu et al. 2011).Metspalu et al. (2011) suggested that the apparent unsuitability of pennycress to M. aeneus and M. viridescens may be due to plant chemistry (e.g., glucosinolates or other secondary metabolites).

Diptera
The serpentine leaf miner (Liriomyza brassicae (Riley) (Diptera: Agromyzidae)) was found to create mines on leaves of pennycress, yellow rocket (Barbarea vulgaris W.T. Aiton (Brassicales: Brassicaceae)) and black mustard growing in the wild in Wisconsin, United States, and in the laboratory with multiple lineages of L. brassicae (Tavormina 1982).The development time of multiple lineages of L. brassicae from oviposition to adults on pennycress was, on average, between 21.3 and 21.6 days (Tavormina 1982).
Some root maggot flies (Diptera: Anthomyiidae) are pests of germinating seeds and seedlings of crops.Cabbage root fly (Erioischia brassicae (Bouche) (currently Delia radicum (L.)) (Diptera: Anthomyiidae)) pupae were found in the soil near pennycress (up to an average of 0.9 pupae per plant) in a field survey of Brassicaceae weeds in the United Kingdom (Finch and Ackley 1977).However, when pennycress plants were inoculated with E. brassicae eggs in a greenhouse experiment, only 2% of the eggs produced pupae; the resulting pupae were smaller than those reared from other plants, and pennycress roots appeared healthy (i.e., not damaged by larval feeding) (Finch and Ackley 1977).In addition, pennycress is a reported host for Delia floralis (Fallén) (Diptera: Anthomyiidae) (Strickland 1938, Savage et al. 2016).Furthermore, adults of seed corn maggot (Delia platura (Meigen) (Diptera: Anthomyiidae)) have been found to be abundant on pennycress flowers (Forcella et al. 2023a).However, the potential impacts of the feeding of D. platura larvae on pennycress seeds or seedlings remain to be evaluated.
Swede midge (Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae)) has been observed to feed on various Brassicaceae weeds including pennycress (Stokes 1953a(Stokes , 1953b), but it was not found on pennycress growing in and near Brassicaceae vegetable fields in New York, United States (Chen et al. 2009).In a no-choice experiment, C. nasturtii oviposited on pennycress, but the number of larvae produced on pennycress was about 4 times lower than on cauliflower (Chen et al. 2009).In an ovipositional choice test experiment with pennycress, cauliflower, and 5 other Brassicaceae weeds, no C. nasturtii larvae were found on pennycress (Chen et al. 2009).

Hemiptera
Aphids have been observed infesting pennycress in Wisconsin and Missouri, United States, and concern has been raised about their pest status for this new crop (Basnet and Ellison 2024).Cabbage aphid (Brevicoryne brassicae (L.) (Hemiptera: Aphididae)) was found to feed on pennycress in a laboratory experiment in Poland (Gabryś and Pawluk 1999).Results of tests using an electrical penetration graph showed that pennycress is an acceptable host for B. brassicae but that the phloem elements of pennycress may contain a deterrent factor (Gabryś and Pawluk 1999).
Turnip aphid (Hyadaphis pseudobrassicae (Davis) (currently Lipaphis pseudobrassicae (Davis)) (Hemiptera: Aphididae)) colonized and fed on pennycress in a series of greenhouse experiments in Iowa, United States (Jarvis 1970).Survival of pennycress plants 3-4 weeks after infestation with H. pseudobrassicae was 66% with no individual plants of pennycress showing resistance to this aphid (Jarvis 1970).In a second experiment, colonization of pennycress seedlings by alate H. pseudobrassicae was about 1/5 that of the average colonization on several susceptible genotypes of B. napus.In a third experiment, the population growth of H. pseudobrassicae on pennycress was about 1/4 that of the average population growth on several susceptible genotypes of B. napus (Jarvis 1970).
The plant bugs (Lygus lineolaris (Palisot), Lygus elisus Van Duzee, and Lygus borealis (Kelton) (Hemiptera: Miridae)) were found on pennycress growing in the wild in Manitoba, Canada (Gerber and Wise 1995).Overwintered adults of L. lineolaris appeared on pennycress during the second and third weeks of May, followed by nymphs in the third and fourth weeks of May (Gerber and Wise 1995).Lygus spp.nymphs remained abundant on pennycress from late May to late June and likely consisted mainly of L. lineolarius (Gerber and Wise 1995).However, by the time pennycress ripened at the end of June, few Lygus spp.remained on the plants, suggesting that this plant stage is unsuitable for Lygus spp.(Gerber and Wise 1995).

Lepidoptera
Bertha armyworm (Mamestra configurata Walker (Lepidoptera: Noctuidae)) survival and development were examined in a laboratory experiment in Canada with neonate first instars placed on excised leaf tissue of 10 plant species from 5 families, but M. configurata did not survive on pennycress (Dosdall and Ulmer 2004).
Southern armyworm (Prodenia eridania (Cramer) (currently Spodoptera eridania (Stoll)) (Lepidoptera: Noctuidae)) larvae were evaluated in the laboratory for feeding and growth on 74 plant species from multiple families in Illinois, United States (Soo Hoo and Fraenkel 1966).Larvae fed on pennycress, but pennycress did not support growth of S. eridania (Soo Hoo and Fraenkel 1966).
Cabbage looper (Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae)) was found to feed on pennycress, broccoli, and 7 other agricultural weeds in a series of experiments with greenhousegrown plants in British Columbia, Canada (Cameron et al. 2007).In a choice test experiment, adults of T. ni showed a preference to oviposit and feed on pennycress compared to broccoli (Cameron et al. 2007).However, in no-choice experiments, first instar T. ni consumed relatively little leaf tissue of pennycress, and less than 2% of those larvae survived after 7 days, whereas survival was greater than 60% on the other plant species (Cameron et al. 2007).Thus, Cameron et al. (2007) suggested that pennycress could be explored as a dead-end trap crop for T. ni management.
The larval growth of P. rapae when reared on pennycress was intermediate among multiple Brassicaceae plants in laboratory studies (Slansky andFeeny 1977, Okamura et al. 2016).Females of P. napi were found to lay eggs on pennycress plants of all sizes in Sweden, but more eggs were laid on smaller (e.g., 5 cm) compared to larger (e.g., 20 cm) plants, and smaller plants seemed to be more advantageous to survival and development of P. napi (Forsberg 1987).
Diamondback moth (Plutella maculipennis (Curt.)(currently Plutella xylostella (L.)) (Lepidoptera: Plutellidae)), which migrates to northern areas each spring, is found on pennycress in early spring in Ontario, Canada, and North Dakota, United States (Harcourt 1957, Kmec andWeiss 1997).Pennycress is a host for the first generation of P. xylostella prior to emergence of cultivated Brassicaceae plants (Harcourt 1957, Kmec andWeiss 1997).Adult P. xylostella in North Dakota were present from May to June in pennycress adjacent to field crops (Kmec and Weiss 1997).The density of P. xylostella eggs on leaves of pennycress varied from about 10-60 eggs m −2 , and egg density was correlated with counts of adult P. xylostella in the field (Kmec and Weiss 1997).In Michigan, Idris and Grafius (1996) found intermediate levels of oviposition, development, and survival of P. xylostella on pennycress compared to several Brassicaceae plants, but similar egg hatches were observed.The average number of eggs per female P. xylostella on pennycress was lower than broccoli but similar to canola and 3 other weeds in a choice test and similar to broccoli, cauliflower, canola, and 6 other weeds in a no-choice test (Idris and Grafius 1996).Developmental time (from egg hatch to pupation) on pennycress (~13-14 days) was similar to red cabbage and several weeds (Idris and Grafius 1996).Furthermore, survival of P. xylostella larvae from hatching through the second instar was ~40% on pennycress, which was similar to red cabbage but lower than broccoli, kale, cauliflower, green cabbage, and canola (Idris and Grafius 1996).Survival of P. xylostella larvae from the third through fourth instar was high on pennycress (~85%) and similar to broccoli, kale, cauliflower, canola, and 2 weeds (Idris and Grafius 1996).The suitability of pennycress and 7 other Brassicaceae weeds as hosts for P. xylostella was examined in China using clip cages on intact leaves (Niu et al. 2014).Development time from egg to adult emergence (20.1 days) was the longest, the pupal weight (females: 4.3 mg; males: 3.1 mg) and survival from egg to adult (48.8%) were the lowest, and female adult longevity (15.1 days) and fecundity (192.4 eggs per female) were intermediate on pennycress compared to the other plants (Niu et al. 2014).Overall, P. xylostella raised on pennycress had the lowest intrinsic and finite rates of increase, longest generation time, and lowest net reproductive rate compared to the other plants (Niu et al. 2014).
Furthermore, pennycress and 3 other flowering plants were evaluated as nectar sources for adult P. xylostella in a laboratory experiment in Alberta, Canada (Munir et al. 2018).The longevity of adult P. xylostella (~25 days) on floral resources of pennycress was similar to that of S. arvensis and B. napus and higher than Lobularia maritima (L.) Desvaux (Brassicales: Brassicaceae), 10% honey solution, or water; however, the weight of P. xylostella adults was lower on floral resources of pennycress compared to L. maritima, 10% honey solution, or water (Munir et al. 2018).

Pennycress Response to Stresses Similar to Insect Injury
The response of pennycress to insect feeding is poorly understood.Some insight into how pennycress might respond could be inferred from how related crops (e.g., rapeseed and canola) respond to insect pests (e.g., Lamb 1989).Furthermore, a more specific understanding of how pennycress responds to insect feeding may be gained by examining the limited research on the response of pennycress to simulated injury (e.g., stand loss, defoliation, and apical stem injury).
Reductions in plant density due to insect feeding can have varying effects on crop yield, depending on the plasticity of the plant's growth (Bardner and Fletcher 1974).A greenhouse experiment was performed in the United Kingdom to examine the response of pennycress to varying initial plant density and subsequent removal of neighboring plants at different timings (Matthies 1990).Pennycress seed was sown in pots and thinned after germination to targeted densities ranging from 1 to 64 seedlings per 12 cm × 12 cm pot (Matthies 1990).Then, for the thinning treatments, all neighboring plants were removed from around a central focal plant in each pot during the vegetative, flowing, and seed pod stages of pennycress (Matthies 1990).In this study, pennycress showed plasticity in response to plant density by producing more seeds per plant and larger seeds as plant density decreased (Matthies 1990).In addition, pennycress showed a greater ability to compensate when the removal of neighboring plants occurred at earlier growth stages (Matthies 1990).
Defoliation can have diverse physiological and morphological consequences on plants that can take place across a broad spectrum of timeframes (Clement et al. 1978, Hammond and Pedigo 1982, Aldea et al. 2005, van Klink et al. 2015).In a greenhouse experiment carried out in the United Kingdom, the effects of defoliation during 2 stages of pennycress flower development were investigated (Pyke 1989).For the defoliation treatments, all leaves on the primary stems of plants were removed when the first flower opened ("early defoliation") or when 50% of flowers had lost their corolla and began enlarging ("mid-defoliation") (Pyke 1989).Early defoliation caused fewer pods on defoliated plants compared to undefoliated plants (Pyke 1989).In contrast, mid-defoliation had no effect on the number of pods but resulted in a greater number of aborted seeds per pod on defoliated plants compared to control plants (Pyke 1989).Pyke (1989) noted that pods with aborted seeds were smaller but remained green on the plants and, therefore, may act as a photosynthetic source for seeds developing in other pods.
Apical injury to stems of plants that produce terminal flowers may result in increased branching from axillary buds and thereby increase the number of flowers but also results in loss of resources in the removed tissue, loss of photosynthetic area, and delays in seed production (Trumble et al. 1993, Fay et al. 1996).In a greenhouse study carried out in Indiana, United States, the impact of apical stem removal and fertilization on the branching and seed production of pennycress was assessed (Benner 1988).Early stem removal was performed when plants started to show internode elongation, and late stem removal was performed when most plants had formed flower buds or open flowers (Benner 1988).When the plants started to show internode elongation 20 days after being transplanted, early treatments involving apex removal and nutrient addition were conducted (Benner 1988).Late treatments, which also involved apex removal and nutrient addition, were performed 30 days after transplanting when most plants had formed flower buds or open flowers, which could potentially affect their response differently from plants that had not yet produced flowering structures (Benner 1988).Removal of the plant apex led to a decrease in the number of primary branches and an increase in the number of secondary and tertiary branches (Benner 1988).These effects were generally more pronounced when the apex was removed earlier than later (Benner 1988).Moreover, the number of fruits produced on all types of branches was higher in the plants where the apex was removed, regardless of the timing, with the early removed plants producing more fruits on these branches than the late-removal ones (Benner 1988).The total weight of seeds per plant was greater for early removal plants compared to late-removal plants, and the total weight of seeds for the control plants was generally greater than that of plants with either removal timing (Benner 1988).Benner (1988) observed that pennycress had some ability to compensate for apical removal by increasing the number of seeds produced but not the size of the seeds.

Beneficial Insects Associated with Pennycress
Natural enemies such as parasitoids and predators could be affected by the incorporation of pennycress into cropping systems.Conflicting results have been observed for the effects of pennycress on Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae), a parasitoid of P. xylostella.In a field study in Michigan, United States, the longevity and fecundity of adult D. insulare females provided floral resources of pennycress was similar to (or slightly higher) than those provided only water and lower than those provided floral resources of B. vulgaris or C. bursa-pastoris, or a honey-water solution (Idris and Grafius 1995).In contrast, in a laboratory experiment in Alberta, Canada, the longevity of adult D. insulare on floral resources of pennycress (~25 days) was higher than on floral resources of S. arvensis, B. napus, or L. maritima, a honey-water solution, or water; however, the weight of D. insulare adults was lower on pennycress compared to S. arvensis, but higher than on water (Munir et al. 2018).In addition, indirect host-mediated effects of pennycress on D. insulare have also been examined.In a laboratory experiment in Michigan, United States, parasitism rates were lower and development times were longer for D. insulare when their host (i.e., P. xylostella) was reared on pennycress compared to several cultivated Brassica spp.(Idris and Grafius 1996).Lipa et al. (1977) documented 9 species of predators associated with pennycress in Europe, including Adonia variegata (Goeze) (currently Hippodamia variegata (Goeze)), Coccinella quatuordecimpustulata (L.), Coccinella quinquepunctata (L.), Coccinella septempunctata L., Coccinella undecimpunctata (L.), Propylaea quatuordecimpunctata (L.) (Coloptera: Coccinellidae), Tachyporus hypnorum F. (Coloptera: Staphylinidae), Nabis pseudoferus Rem.(Hemiptera: Nabidae), and Aeolothrips intermedius Bagn.(Thysanoptera: Aeolothripidae).In the Midwest United States, Forcella et al. (2023a) found that adult Syrphidae were common visitors to pennycress flowers; however, the abundance of the predatory larvae of Syrphidae on pennycress was not quantified.In addition, the incorporation of pennycress into crop rotations may favor predatory insects.In a field experiment in Germany, a double-cropping system of pennycress and corn resulted in higher species richness and abundance of predatory ground beetles and higher species richness and diversity of spiders compared to 2 or 3 other common cropping systems (Groeneveld andKlein 2015a, Groeneveld et al. 2015b).
The early flowering time of pennycress can provide a source of early season floral resources to pollinators when most plants have not yet bloomed (Evangelista et al. 2017).The communities of pollinating insects associated with pennycress have received considerable attention (Mulligan and Kevan 1973, Groeneveld and Klein 2014, Eberle et al. 2015, Hassall et al. 2017, Stavert et al. 2018, Thom et al. 2018, Forcella et al. 2021, 2023a, 2023b).

Conclusions
Pennycress has the potential to provide multiple benefits as a cover and oilseed crop in corn-soybean rotations in the Midwest United States.Significant advances have been made with genetic improvements and agronomic practices for this crop.However, as this crop begins to be adopted by farmers, there is an urgent need for guidance on potential pests, impacts of those pests, and management strategies.
To our knowledge, insect herbivore communities associated with pennycress grown as a crop or cover crop have not been fully documented.To provide a foundation for understanding potential insect pest threats, the scattered knowledge about insects associated with pennycress was compiled in this review.Among the taxa found associated with pennycress, several taxa, including Phyllotreta spp., Aphididae, Lygus spp.and P. xylostella, may pose the greatest pest threats to pennycress.However, because the primary focus of those studies was on pennycress growing in the wild (natural systems) or as a weed in agricultural systems, further work is needed to characterize the insect herbivore communities associated with pennycress growing under monoculture or intercropping scenarios representing how this crop will be deployed on the agricultural landscape.For example, seed maggots (Diptera: Anthomyiidae) are attracted to the flowers of pennycress (Forcella et al. 2023a), but it remains unknown if this might lead to increased abundance of such pests attacking seed of crops relay cropped into pennycress.Furthermore, as the domestication of pennycress continues, the susceptibility of new pennycress genotypes to insect pests will need to be evaluated.
Finally, we are not aware of any published reports regarding how pennycress responds to injury from insects.However, limited studies showing responses of pennycress (including yield loss or compensation) to reduction in plant density, and artificial defoliation and stem injury provide some insight as to how it might respond to insect pests.Further work is needed to examine the response of pennycress to actual and simulated insect injury.Such information will provide a foundation for the development of management guidelines such as economic injury levels and economic thresholds.
et al. (1977)  were made primarily from Poland but may also represent observations from Czechoslovakia, Germany, and Hungary.c Life stages: A = adults, E = eggs, L = larvae, N = nymphs, P = pupae.d Plant parts: S = stem, L = leaves, R = root, F = flower, O = occasional, SP = seedpod.